Quartz-to-metal seal



Patented Mar. 3, 1953 QUARTZ- TO -METAL SEAL LoB. Peters, Cleveland Heights, Ohio, assig norto General Electrie Company, a. corporation of NewYork ApplcationJ une 19, 1951; Serial No 232 ;332

4 Clains.; (Cl. I'M-50.63)

My. invention. rel-ates to. quartz-to-metal seals fort electric.: devices suchtias. el-ectric discharge lamps.

In my oopending applioation Serial No. 24,522 filed? May 1, 1948 I have described a quartztometal seal of high capaci'ty and of small size and simple structure using but one large conduoton such as.-a tungsten rod, for: carrying the current and passing through the quartz partgof the :seaL Thequartz is-no t fused to the rod; rather, a\ seal memberin'the form of a thin molybdenum disc around the rod and hermetically united therewith is provided. The disc has a thin feathered peripheral edge imbedded in the quartz and to which the\ quartzvis used'to make a gas tigh-t joint. The hermetie joint .between the molybdenum disc and thetungsten. rod is constituted by anialloy of these two metalsvand platinum.

As; diselosed in my oopending application such seals are made in the form of stems for the quartz envelopes. of high .pressure mercury vapor dischargeolamps having a power Consumption of the order of kilowatts 'and a vapor 'pressure of many atmospheres.

An object. of the present inventon is to. providea sealiof the above -typewherein discs of greater thio'kness may be herm etieally united with the quartz to increase the strength of the stern without increasing the risk of fracture of theseal. or of the stem. Another object of the invention is to provide a method of making such aeseali. Still further. objectsand advantages. attaehing to .the invention and to its use .and operation will be ap parent 'from the` following; de,- taileddescription of species thereof.

Inothevaceomp-anying drawingan emboxdimen-t oftvthe invention, is shownin which F'g. 1 is an elevational, partly sectional View of a stern having a seal structure embodyingmy invention; Fi'g.' 2.is a fragmentary partly sectional'view on an enlarged s-cale of the assembled seal portion of the stern and Fig. 3 isa similar view of one half of the disc assembly of the steme Refer ring to Fig. 1 the stem eom p-rises aquartz stern tube I having a conductor rod 2 extending therethrough. Thin molybdenum f-oil sleeves- 3, the thickness of which is exaggerated in the drawing, are Wrapped around the'rod '2 to prevent the quartz fusing with and adhering to the rod during fabrication of the stem. A molybdenum disc 4 is positioned around the rod 2 and its thin tapered peripheral sealing edge is `imbedded in the vtreous wall of the stern tomake-a gas tight joint. The disc `4 is cup shaped to relieve the radial strans set up therein because of the'.

difierent rates of exp ansi on of-therod-2, the disc 4 andthe vitreous part of the stemund-ermanu facturing and servioeoonditions.

The: stern tube I is .provided. with a fLare 5 `at one end thereof -or fusion with the sides of an opening in a quartzenvelope to close said opening with the electrode '6 mounted-on rod 2 within the envelope. When the envelope istha-t of an electric -discharge lamp Operating-at; an elevated temperature, the joint betweenthe dise-A and the rod 2 must be gas tght a t temperatures ranging from room temperatureto perhaps hundreds of degrees centigrade. As discl-osed in 'my copendng application referred to above 'I have found that -a brazed platinu m joint meets these requiremen ts and is mechancally strong enough to :withstand p-ressures of many atmospheres at such temperatu-res. The brazed joint is shown at 'I in Fig. 2 of the drawing and is -on the side of the disc 4 away from the fiare.

In order to ninirnize mech-anicalstran between the peripheral edge of the disc 4 and the quartz--portion of the stem I interpose between and hermetically unite with these members during manufaetu-reof the stem-vitreous material having a coefiieien t of expansion between .that of quartz and thatof molybdenum. The disc 4 may then be of gra-ater thi ckness and greater mechanical s-trength to increase the streng th of the stern. As shown in Fig. 2 of the drawing, this vitreous material is in the for-*moi .a pair of annular wafers 8 which aremounted around the ,rod 2 in opposing positions with respect to dsc .4 during assembly of ;the stern., The wafers 8 are of larger outside diameter than the disa/4 so that the latter is completely -co-vered the-reby, in the -completed stern.

The assembly including the foil covered rod 2, the dsc 4 hermetioally united therewith by 'the brazed joint 1, and the wafers '8 positioned as shown in Fig. 2, also includes 'a molybdenum ol manufacture of the stem just as the foi1 3 prevents the quartz portion of 'the stern stieking to the rod 2 toavoid fracture of the stern.

The foil covering for the side of thedsc 4 facing toward the flare 5 is a single annular sheet or Washer 9 (Figs. 2 and 3) extending from the rod 2 outwardly to the inner edge of the tapered portion ll!` of the disc 4. The foil covering for the side of disc 4 facing away from flare 5 and the brazed joint 'l is made up of a number of annular, .overlapping sheets oriwashers (Figs. 2 and 3) to provide a greater cushioning action between the joint 'I and the cup shaped portion of disc 4 on one hand and the opposed wafer 8 on the other. The first of the said sheets, sheet ll, extends from adjacent the rod 2 to the end of the tapered edge lil of the disc 4 so as to cover the inner surface of the cup shaped portion of the disc 4 and part of the joint 'L The intermediate annular sheet z overlays the inner portion of the sheet l I and terminates on the bottom of the cup shaped portion of disc 4. The annular sheet !3 extends from the rod 2 partially over the sheet I 2 and terminates short of the peripheral edge of the latter.

In making the stem the above describedas sembly of the metal parts thereof with the waiers 8 is mounted within a pair of flared quartz tubes !4 and |5 by inserting the ends of the foil covered rod 2 in the bores of the tubes 14 and l5-. The flares s and I' of the tubes M and !5, respectively, are of larger diameter than the disc 4 and the wafers 8 and one of them, fiare !1, has united therewith a quartz cylindrical ring member !8 slightly larger in diameter than the flares and extending a suflicient distance from flare l'l to cover the gap between the flares !6 and IT and to overlap the periphery of the flare !6 when the elements making up the stem are assembled as shown in Fig. 2.

With the stem Components assembled as shown in Fig. 2 an inert gaseous atmosphere, such as nitrogen, is caused to flow inward from the outer ends of the quartz tubes M and |5 to free the interior of the assembly from air and fill it with inert gas. The quartz ring I8 is then heated by the usual gas flame to Collapse it onto and join it with flare !6 while a gentle flow of the inert gas is continued to exclude from the interier of the assembly contaminating gases from the flame.

The fiame is defiected by the ring !8 away from r the surfaces of the ring [8 and the fiare 16 to be united.

After ring !8 and flare !6 have thus been hermetically united the flow of inert gas is discontinued, the interior of the assembly is evacuated and the flares [6 and ll are heated to their softening temperature. During heating of the flares [6 and IT the wafers 8 are also heated by heat from the flame transmitted thereto through the ring !8 and flares [6 and l'i. The wafers 8 are of a selected vitreous material having a softening temperature about 200 C. less than that of quartz so that when the flares [8 and l'l have been softened sufficiently to unite with each other the wafers 8 are soft enough to unite with the peripheral edge portion ID of the disc 4 to make a gas-tight joint therewith.

When the quartz flares !6 and Il and the wafers 8 have been heated to their softening temperature as describedvabove the tubes M and |5 are moved toward each other along the rod 2 to force the flares I& and ll against the waiers 8 and the latter against the sealing edge portion ill of the disc 4 to hermetically unite these members together. The peripheral portions of the flares IB and l'l extending beyond the wafers 8 are also joined to each other during this step in the method.

The heating is continued and the heating flame is directed so as to collapse first the portions of flares IB and l'l opposite the foiled covered portions of the disc 4 and the joint 'I and then the body of tubes 14 and !5 is collapsed onto the foil covering 3 of rod 2. This increases the P mechanical strength of the stem. The flame is '4 then removed from the stem, the vacuum pump is disconnected therefrom and the stem is allowed to cool. The electrode 6 may then be mounted on the rod 2, as by welding, to complete the stem assembly.

In a stem having the Construction described above and made by me the molybdenum disc 4 was inch in outer diameter and .005 inch thick at its cup shaped portion which was .02 inch deep and 1 2; inch in diameter. The peripheral or scaling edge portion !0 of disc 4 was etched to a thickness of .002 inch at a distance of 1 mm. from its outer end and to a thckness of .004

inch adjacent the rim of the cup shaped por- -'tion. The annular sheets 9, ll, [2 and |3 and the foil sleeves 3 were .0007 inch thick. The sheet !2 overlaying the inner portion of sheet p ll was 1%; inch in outer diameter and the sheet !3 Was A; inch in outer diameter. The rod 2 Was inch in diameter and the wafers 8 were approximately .04 inch in thickness. I have demonstrated that discs having a thickness of .007 inch at the cup portion and .005 inch at the heaviest portion of the sealing edge in contact with the wafers 8 may be successfully used in the new stem. In contrast, when the wafers 8 are omitted the thickness of the sealing edge portion of the disc united with the quartz cannot exceed .0025 inch.

While vitreous material of many different compositions having suitable softening tenperatures and coefiicients of expansion may be used for waiers s, I prefer the material designated in the trade as 7911 "Vycor" which has approximately twice the thermal coefcient of expansion of quartz, a soitening point more than 200 C. less than quartz and which contains 96% silica by weight. When desired, the rod 2 may consist of molybdenum or of a mixture of, tungsten and molybdenum, and the disc i may consist 'of tungsten or a mixture of tungsten and molybdenum with appropriate modification of the dimensione of the disc.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A stem for a high pressure mercury vapor discharge lamp comprising a quartz stem tube, a refractory metal scaling disc within said tube and hermetically united around said conductor. said disc having a tapered sealing edge, said stem comprising also a vitreous material interposed between said disc and said quartz stem tube and hermetically united with said tube and with the tapered edge of said disc, said material having a coefiicient of expansion between that of said disc and that of quartz and a softening temperature of the order of 200 degrees centigrade less than that of the quartz, the maximum thickness of the said tapered sealing edge of said disc united with said vitreous material substantially exceeding the maximum permissible thickness of the corresponding portion of a similar disc having its sealing edge hermetically united directly with quartz.

2. A stem for a high pressure mercury vapor discharge lamp comprising a quartz stem tube, a refractory metal conductor extending through said tube and a 'efractory metal scaling disc within said tube and hermetically united around said conductor, said disc being cup shaped at its center portion and having a tapered peripheral sealing edge, a refractory metal foil sheet covering the outer surface of said cup shaped disc portion and a plurality of similar overlapping sheets of decreasing diameter covering the inner surface of said cup shaped portion, said stem comprising also a vitreous material interposed between said disc and said quartz stem tube, said material being hermetically united with said stem tube and to the peripheral portion of said disc and having a coefficient of expansion between that of said disc and that of quartz and a softening temperature of the order of 200 degrees centigrade less than that of the quartz, the maximum thckness of the said tapered scaling edge of said disc united with said vitreous material substantally exceeding the maximum permissible thickness of the corresponding portion of a similar disc having its scaling edge hermetically united directly with quartz.

3. The method of making a quartz-to-metal seal of the type having a quartz stem tube, a refractory metal conductor extending through said tube and a refractory metal sealing disc within said tube and hermetically united around said conductor which comprises the steps of mounting on the conductor and in opposed positions with respect to the disc a pair of annular wafers of vitreous material having a lower softening temperature than quartz and a coefiicient of expansion between that of quartz and that of the refractory metal of the disc, mounting the ends of the conductor in quartz tubes having fiared inner ends so that the peripheries of said flared tube ends, said wafers and said disc are juxtaposed, heating the peripheries of said fiares to the softening temperature of quartz while maintaining a non-oxidizing atmosphere about said disc and moving said ares together to hermetically unite said fiares to each other and to said wafers and to hermetically unite said wafers to said disc.

4. The method of making a quartz-to-metal seal of the type having a quartz stem tube, a refractory metal conductor extending through said tube and a refractory metal scaling disc within said tube and hermetically united around said conductor which comprises the steps of covering said rod and the center portion of said disc with molybdenum foil to prevent the vitreous components of the stem sticking to said rod and said disc, mounting on the conductor and in opposed postions with respect to the disc a pair of annular wafers of vitreous material having a lower softening temperature than quartz and a coefiicient of expansion between that of quartz and that of the refractory metal of the disc, mounting the ends of the conductor in quartz tubes having flared inner ends so that the peripheries of said flared tube ends, said wafers and said disc are juxtaposed, heating the peripheries of said fiares to the softening temperature of quartz while maintaining a non-oxidizing atmosphere about said disc and moving said flares together to hermetically unite said fiares to each other and to said wafers and to hermetically unite said wafers with said disc and then heating and collapsing said quartz about the foil covered portons of said disc and said rod to make a mechanical joint therewith strengthening said stem.

LEO R. PETERS.

REFERENCES CITED UNITED STATES PATENTS Name Date Greiner Apr. 18, 1950 Number 

